The invention relates to a bi-directional speed reducing mechanism and more particularly to a bi-directional mechanism for use with hand-held power tools having separable motors and gear heads between which the instant invention may be mounted. The bi-directional speed reducing mechanism of the instant invention also achieves a reduction in output speed in the range of from 3.5:1 to 9:1 with a concommitant increase in output torque.
The dictates of mass production have resulted in great dependence upon the production line method of manufacturing and this dependence has in turn necessitated the development of a broad scope of lightweight, hand-held power tools for use by assembly personnel on the production line. Generally, these tools are powered by either compressed air or electricity. A relatively simple high r.p.m. motor driven by either of these energy sources may be linked to such various output devices as gear trains, ratchet mechanisms and the like to adapt the power source to a broad variety of requirements associated with various assembly operations.
A frequent requirement of such power tools is the capability of reversing the direction of output in order to facilitate, for example, the removal of a threaded fastener which may have been partially or improperly inserted or which must be removed to disassemble a component.
In hand tools powered by electricity, reversal of the electric motor is a somewhat more difficult problem than is immediately apparent. It is well known that reversing the polarity of electrical power supplied to certain windings in the motor will reverse the direction of rotation and that this polarity reversal can be achieved by simple switch mechanisms. Unfortunately, the mechanical shock associated with a high speed reversal to which the motor rotor is subjected as well as the electrical transients and back e.m.f. generated during the reversal operation to which the switching mechanism is subjected generally shortens the service life of the tool and lowers its reliability.
In tools driven by compressed air, the means most commonly utilized to provide bi-directional rotation is a vane motor having two inlet ports symmetrically disposed on opposite halves of the vane motor chamber and a single exhaust port positioned equidistant from the two inlet ports. Compressed air entering one inlet port and exiting the single exhaust port causes the vane motor to rotate in one direction whereas air entering the other inlet port and exiting the single exhaust port causes rotation of the vane motor in the opposite direction. A major drawback of a reversible air motor of this design is its reduced power output. Since the air must enter, expand and exit the vane motor in less than one hundred eighty degrees, the recovered energy and thus the power produced by the air motor is less than that which can be produced in a conventional unidirectional motor wherein the circumferential separation between the inlet and outlet ports permits effective utilization of the expensive power of the air over approximately two hundred forty degrees. Thus, a bi-directional air motor of this design is less efficient and produces less power than a comparable unidirectional motor.
The common alternative to utilizing a bi-directional air or electric motor in a hand tool comprehends incorporating a separate mechanism in tandem with the motor for providing a selectively reversible output. Generally these devices also exhibit somewhat reduced power output when compared to the output of a unidirectional power tool. In this case, the power reduction is due to the additional mechanism, typically gearing, in the reversing device. Such add-on reversing devices typically increase the weight of the power tool by a substantial amount. On the production line, where an operator may lift, move and position the tool constantly for several hours, such additional weight dramatically increases worker fatigue. The size of the tool is also an important consideration since it is often necessary to position and operate the tool within the structure being assembed such as, for example, a door or fender well of an automobile. A tool having the requisite reversing capability may, however, be rendered marginally or totally unusable in a given application if, due to its bulk and lack of maneuverability, it cannot engage or cannot easily be manipulated to engage a given fastener.
A production process that requires rotational speed substantially below that of the motor output and high torque as well as bi-directional rotation will generally require an even more complex mechanism. Components in addition to those necessary to produce a bi-directional output may be required and the size and weight of the reversing mechanism may then seriously limit its use as a production line tool.